An apparatus of this kind is known, for instance from U.S. Pat. No. 787,717. A double arm flyer which carries yarn guide elements in the form of yarn eyes is freely rotatable on a cylindrical tang, which is coaxial with the spool, and is provided with a brake in the form of a helical spring, which offers a predetermined adjustable resistance to the rotation of the flyer arm. Since neither the spool nor the flyer arm is driven, a certain tensile force must be applied to the spooled yarn in order to unwind it; this tensile force depends on the braking torque exerted by the brake, among other factors. With delicate spooled yarn or highly elastic spooled yarn, for instance, it is no longer readily possible to generate the relative movement between the flyer arm and the spool by means of a tensile force generated in the spooled yarn. The unvending process becomes uneven, especially if the spooled yarn must be pulled off the spool at a variable travel speed. Further, the parts set to rotating by the pulled-off spooled yarn have considerable inertia, which means that when the travel speed of the pulled-off spooled yarn changes, the tension on the yarn fluctuates, and this is inappropriate or impermissible in many applications. regardless of the tension that is maintained in the spooled yarn, thereby protecting against unevenness in the tension of the unwinding spooled yarn. At the same time, the spooled yarn itself is handled gently, because it need not absorb any tensile stresses needed for the unwinding. The spooled yarn can be pulled off at any arbitrary adjustable tension; yarn pull-off is even readily possible with a zero tension.
If the amount of spooled yarn removed varies greatly over time, elongations can occur briefly in the spooled yarn, in the area between the sensing means and the spool; often, these elongations can be absorbed by the inherent elasticity of the spooled yarn. If a special yarn does not allow this, it is useful to provide a yarn reserve on the yarn path between the spool and the sensing means. In this case it is advantageous if the apparatus has a regulator which maintains the size of the yarn reserve at a command value. (See referenced application Ser. No. 759,653, filed July 26, 1985, Memminger and Roser, now U.S. Pat. No. 4,673,139).
In a preferred embodiment, the arrangement is also such that the apparatus has adjustable tensioning means controlling the tension of the spooled yarn unwinding from the spool. These tensioning means are located along the spooled yarn path between the spool and the sensing means. If necessary, a spooled yarn tension regulator then maintains the tension on the spooled yarn automatically at a predetermined command value can be coupled with these tensioning means.
The drive motor is advantageously a stepping motor, which is supplied with the output signal of the sensing means, which if necessary is converted into a corresponding stepping pulse train and amplified. Alternatvely, in particular with spooled material that is difficult to handle, such as cables or wire, the apparatus may also be so formed that it has a servo regulator that continuously readjusts the speed of the drive motor, which in particular is formed as a stepping motor, to the output signal of the sensing means, which acts as a command value.
Very simple structural conditions are attained if the sensing means are formed by a low inertia measuring wheel coupled in a slip free manner with the spooled yarn and combined with a signal transducer. This signal transducer may be in the form of a tachometer generator, which emits an analog voltage, an angle code reader, or the like.
The tensioning means suitably have a movable tensioning element acting on the spooled yarn between the spool and the sensing means, transversely to the yarn travel direction, and loaded with an adjustable force. This force may be provided by a weight, a spring force, an electromotor force and/or a centrifugal component.
Since the sensing means already furnish an output signal representative of the spooled yarn travel speed, this output signal can simultaneously also be used to supply a display device for displaying the quantity of unwound spooled yarn per unit of time. The display device may at the same time include a display for the tension of the furnished yarn, as measured by a spooled yarn tension measuring device.
If the spooled yarn should have lost its tension, for instance because of yarn breakage and subsequent retying of the yarn, or for other reasons, or if the yarn is sagging in the vicinity of the flyer arm, then before the unwinding operation can be resumed it must first be made taut. This can be done in a simple manner by coupling a rotation reversal switch with the drive motor. By the simple actuation of this rotation reversal switch, the spooled yarn is wound onto the spool until the conditions necessary for resuming the unwinding operation are reestablished.
The arrangement can also be such that a tension monitor is coupled with the drive motor, and if the spooled yarn tension drops below a predetermined threshold and there is an interruption in the unwinding of spooled yarn, this tension monitor emits a signal that reverses the drive motor, causing the drive motor to generate a relative rotation between the flyer arm and the spool in the direction of yarn rewinding, until the predetermined spooled yarn tension value has been attained.
The term "spooled yarn" is intended to encompass all kinds of material that can be wound up, such as yarns, filaments, and fiber strips, but also wire and the like. The sensing means for the spooled yarn travel speed may, instead of the measuring wheel mentioned above, be of some other kind as well, including means capable of scanning the spooled yarn without touching it.
The apparatus is particularly intended for pulling spooled yarn from a spool. However, it may equally well be used for winding spooled yarn onto a spool, in which case it is assured that the spooled yarn is always wound up at a predetermined tension.
Naturally a traversing movement back and forth in the axial direction between the spool and the flyer arm can also be provided during the winding or unwinding operation. The mechanisms required to effect this movement are known and are accordingly not described in detail here.